Acta Hortic. 1292. ISHS 2020. DOI 10.17660/ActaHortic.2020.1292.17 XXX IHC – Proc. Int. Symp. on Fruit and Vegetables for Processing Ed.: M.A. Koyuncu 129 Investigating the effects of pre-treatment and thin layer drying methods on quality of mango slices K. Mugodo 1,a , T.S. Workneh 2 and S. Sibanda 1 1 Agricultural Engineering, Agricultural Research Council, Pretoria, South Africa; 2 School of Engineering, University of Kwa-Zulu Natal, Pietermaritzburg, South Africa. Abstract Fresh Mangifera indica L. ‘Tommy Atkin’ with flesh colour parameters, of L* (47.70±5.6), a* (24.72±6.9) and b* (34.87±8.76), a mean TSS of 13.85±2.07 °Brix and firmness of 4.4±3.2 N were used for the drying experiments. This study investigated the effect of three drying methods, namely, open-air solar drying (OAD), modified ventilation solar drying (MVD) and convective oven drying (OVD) on quality parameters of 3, 6 and 9 mm mango slices with and without lemon juice pre-treatment. The study observations found relatively high colour changes on mango slices dried in OAD than for MVD and OVD. Thicker mango slices (9 mm) dried in OAD were darker, indicating that there was more browning, compared to the thinner slices (3 and 6 mm) which were dried in MVD and OAD. Sensory evaluations showed that panellists preferred treated mango samples. The overall acceptability of pre-treated mangoes dried with MVD (7.09±1.26) was not significantly higher (P>0.05) than that of mangoes dried in OVD (6.94±1.64) and OAD (6.51±2.07), respectively. In addition, the microbial counts showed that the dried mangoes were safe for human consumption, as pathogens were not detected. However, fungi and anaerobic bacteria counts were higher than the international stipulated limit of 1×10 3 CFU g -1 . Keywords: solar drying, thickness, colour, microbial count, sensory evaluation INTRODUCTION Drying is a simultaneous heat and mass transfer process, where internal stresses in the food result in physical changes, such as, colour and the loss of rehydration ability (Lewicki and Pawlack, 2003; Karim et al., 2008). It is one of the most cost-effective preservation methods for fruit and vegetables and hot air is commonly used as a drying medium. Popular hot air drying methods include solar drying and convective drying. Open-air uncontrolled solar drying (OAD) has been used for preservation of fruit and vegetables in hot climatic regions, such as South Africa, rather than canning, mainly due to energy savings of the solar energy. Perumal (2007) highlighted that the quality of OAD dried products deteriorates to levels that are not suitable for human consumption. Investigations into convective oven drying (OVD) show that a lower drying temperature of about 60°C, higher drying temperatures above 80°C and longer drying periods results in relatively higher total colour changes (ΔE) and a lower dehydration ratio of mangoes (Akoy, 2014). In addition, OVD competes with the distillation method, as both require high-energy input, due to, the use of hot air at relatively high temperatures. The massive quality losses due to OAD, coupled with relatively higher energy costs of OVD methods have resulted in consideration of other drying methods, such as the use of a greenhouse solar dryer, with modified ventilation (MVD). The concept of using solar energy for large-scale drying operations is increasing because of the concern about the depletion of fossil fuels and their effect on the climate (Perumal, 2007). Dried Mangifera indica L. ‘Tommy Atkin’ is a preferred healthy snack in South Africa, with a potential for export. Research studies report that drying methods used for fruit and a E-mail: mugodok@arc.agric.za; seyoum@ukzn.ac.za